Piperidines as hypergolic fuels



PIPERIDINES AS HYPERGOLIC FUELS Cleveland R. Scott, Arnold L. Ayers, andJohn E. 'Mahan, Bartlesville, kla., assignors to Phillips PetroleumCompany, a corporation of Delaware No Drawing. Application December 4,1951, Serial No. 259,896

Claims. (Cl. 60-35.4)

This invention relates to rocket propellants. 'In one of its specificaspects this invention relates to hypergolic fuels and their applicationto the propulsion of rockets.

Our invention is concerned with new and novel rocket propellants andtheir utilization; a rocket or jet propulsion device, being definedherein as a rigid container for matter and energy so arranged that aportion of the matter can absorb the energy in kinetic form andsubsequently be ejected in a specified direction. The type rocket towhich our invention is applied is that type of jet propulsion devicedesignated as a pure rocket, i. e., a thrust producer which does notmake use of the surrounding atmosphere. A rocket of the type with whichour invention is concerned is propelled by introduction of a propellantmaterial into a combustion chamber therein, and burning it underconditions that will cause it to release energy at a high butcontrollable rate immediately after :entry into the combustion chamber.Rocket propellants, as liquids, are advantageously utilized inasmuch asthe liquid propellant material can be carried in a light weight lowpressure vessel and pumped into the combustion chamber, the latterthough it must withstand high pressure and temperature, being onlynecessarily large enough to insure combustion. Also, the flow of liquidpropellant into the combustion chamber can be regulated at will so thatthe thrust, continuous or in intermittent bursts of power, can besustained, the latter type of liquid propellant flow contributing to alonger life of the combustion chamber and thrust nozzle.

Various liquids and liquid combinations have been found useful as rocketpropellants. Some propellants consist of a single material, and aretermed monopropellants. Those propellants involving two materials aretermed ibipropellants" and normally consist of an oxidizer and a fuel.Hydrogen peroxide and nitromethane are each well known monopropellants.Well known bipropellants include hydrogen peroxide. or liquid oxygen asthe oxidant with a fuel component such as ethyl a1- cohol-water,ammonia, hydrazine, or hydrogen; and nitric acid as the oxidizer withaniline or furfuryl alcohol as the hypergolic fuel component.

When employing 90-100 percent, or more, nitric acid, i. e., white fumingnitric acid as the oxidizer in a rocket bipropellant, it is oftennecessary, dependent on the specific fuel component, to make ignitioninore prompt by dissolvingfrom 6 to 14 percent by weight nitrogendioxide in the white fuming nitric acid forming thereby red fumingnitric acid. A fuel component of a bipropellant material of the typedescribed herein, is spontaneously ignited upon contacting the oxidized,and for that reason is referred to herein as being hypergolic. A ratioof oxidizer to hypergolic fuel based on stoichiometric amounts can beutilized within the limits of 0.5 :1 to 1.5 :1 if desired, theefliciency of the combustion being less at ratios below 1:1 and the useof the oxidizer being less economical at ratios above 1:1. However,practical consideration may necessitate the use of higher ranges, evenas high as 6:1.

2,771,737 Patented Nov. 27, 1956 ROB RCIlR ERROR R C R wherein R is ahydrogen atom or a hydrocarbon radical having not more than 12 carbonatoms and wherein the total number of carbon atoms present in theformula is not greater than 17. R may be a hydrogen atom or ahydrocarbon radical selected from the group consisting of alkyl,alkenyl, aryl, cycloalkyl, cycloalkenyl, aralkyl and alkaryl radicals,the alkyl radical being preferred, especially those having not more than3 carbon atoms. As a preferred embodiment of our invention thehydrocarbon substituted piperidines should contain at leastone hydrogenatom attached to each of the piperidine ring carbon atoms, that is, atleast one R attached to the carbon atoms in the above-describedstructural tormula is a hydrogen atom.

Illustrative of the hypergolic hydrocarbon substituted piperidines ofour invention are 2 me'thylpiperidine, 2,3- dimethylpiperidine and 2,4dimethylpiperidine. Other hydrocarbon substituted piperid-ines such as2,3,4,5-tetrarnethylpiperidine; 2,2-dimethylpiperidine;Z-ethylpiperidine; Z-phenylpiperidine; 4-benzylpiperidine;2,5-tertbutylpiperidine; 2cyclopropylpiperidine; 2,5cyclopentenylpiperidine; 4-cumenylpiperidine are suitable as well astheir higher and lower molecular weight homologs. Particularly suitableare the 2-alkyl substituted and the 2,5alkyl substituted piperidines.Piperidine itself is also especially suited in our invention.

These compounds are well known in the art. The commonest method for thesynthesis of these piperidine compounds is by the reduction of thecorresponding pyridine derivatives. Under special circumstances,however, catalytic methods have almost entirely replaced the earlierused reduction with sodium and alcohols, see Heterocyclic Compounds,Elderfield, vol. I, published by John Wiley and Sons Incorporated, page631 et seq. the disclosures of which are relative 'to the production ofthe piperidines of this invention and are incorporated into and madepart of this disclosure.

These piperidines are hypergolic per se and are also hypergolic whenadmixed with non-hypergolic materials, particularly hydrocarbons, evenin a state of dilution as high as 20 to 30% by volume and in some casesup to by volume and higher. Suitable non-hypergolic diluen'ts includethenormally liquid hydrocarbons orlirixtures thereof, particularlyhydrocarbon fuels in the gasoline boiling range, jet fuels, n-heptane,benzene, kerosene, isooctane, diisobutylene, methylcyolohexane, toluene,and the like.

Other suitable oxidizers or oxidants for these hypergolic fuels inaddition to white or red fuming nitric acid can be used in thebipr-opellant fuel compositions of our invention. These suitableoxidants include materi-alssuch as hydrogen peroxide, ozone, nitrogentetroxide, oxygen and mixed acids, especially anhydrous mixtures ofnitric and sulfuric acids such as -90 percent by volume white orxredfuming nitric acids and 20 10 percent by volume anhydrous or fumingsulfuric acid. It is within the scope of this invention to employpreferably dissolved in the oxidizer-,1ignition-catalysts or oxidationcatalysts. These oxidation catalysts include certain metal salts;suchcas the chlorides andnaphthenates .ofiiron, zinc, cobalt andsimilanheavy metals.

The advantages'of thisinvention are illustrated in the followingexample. The reactants and their proportions andrtheirspecifictingredients are presented as being typical and .should not:be=constr.uedito limit therinvention.

EXAMPLE I Each of the piperidines described hereinbelow was tested forspontaneous ignition employing fuming nitric acid as the oxidizer. Ineach test 1 part by volume of a mixture of a selected: piperidine andn-heptane was dropped into a vessel containing 2.3 parts by volumefuming nitric acid. The mixture of the selected piperidine and n-heptanecoming into contact with the fuming nitric acid ignited spontaneously.Normal heptane was employed as a diluenttodetermine the maximum amount.of dilution a piperidine could tolerate and still retain the propertyofbein'g lhypcrgolic. Tests were conducted at room temperatt re, aboutf70?F. Theresult's are set forth in Table I. T dbleiil Maximum Compound,Oxidant (Dilution,

' Percent n-heptnne 'Piperidine Red Fuming Nitric Acid Ignition.

D White Fuming Nitric Acid Do. I

Red Fuming Nitric Acid Wihite Fuming NitrieAcid Red Furning Nitric AcidWhite Fuming Nitric AcicL'... Red Fuming Nitric Acid.;.... White FilmingNitric Acid.

10. Ignition.

Do. 1 Do. 1

o 2,4-Dimethylpiperidine Der.

I No dilution.

As an=addedfeatureof this inventionthe piperidines of this invention.are alsosuseful for providing vfast, burning fuelsvsuitable fon use inrocket engines and the like where a hypergoliezfuel is not necessarilyrequired. For example, the/fuel componentsof this invention dissolvedina liquid'hydrocarbomsuch as. gasoline, a jet; fuel,'.a kerosene, .arnaphtha. oraa petroleum-fraction having a boiling point usually notgreater ;than 80.0";1-1, even if the resultingzsolutionnis vnothypergolicn with an ,oxidantsuch as fumingtnitric .acid, .can: be usedtogether with an oxidant andi-a suitableigniter as a rocket propellant;These fast burningrfuels areparticularly useful if, forvariousreasons,:=a:?hypergolic,fuel is not desiredor required Thepiperidines;of this invention maybe-addedjtoahydrocarbon liquid in aminor amo t, usu ly rom. a out 1 to;'20% by, ,volumez-of the, totalvmixture to, produce fast burning f uelst Suitable;fast burning fuels;are 1+20% by volllmfi PiPridine.-and 8099%i by Volume of a;petro,- leumfraction in the gasoline boilingrange, ,1;20%; by volume.ZrfllfithYllDjpBE-idinofllld 80 9 9%by volume gasoline, I 1 2 0 h by"volume ,2, 3 -or- 2,4-dimethylpiperidino and,.8 -v 99 %t by-volumegasoline,

As willbeievident to thoseskillediin the art, variousmodificationsicanbe madeor followed, inathfi light of the t g gdisclosure and; discus ion. withont depart ng.

piperidine characterized by thestructural formula;

s R m Ron RQR,

wherein R 'is selected from the group consisting of-=a-hydrogen atom anda hydrocarbonradical sele'etedfrom; the

group consisting-of alkyl; alkenyL ar-yl, cycloalkyd; cycloalkenyl;aralkyland alkarylradicalshaving not more than 12car-bon atoms andwherein the-total numberof carbon atoms presentin-saidformula-is notgreater thannl'Z; 1 "I 2. The method of claimlwhereinsaidifuelicomponent is dissolved in: a -non-hypergolic\ liquidihydrocarbom.

3.- The meth'od' of claim =1 wherein said :hydrocarbon radical containsnot'more-than three carbon:atoms;-\

4; Themethodof claim l whereinisaid fuelacomponent is piperidine.

55-Themethod of claim 11 wherein said fuelcomponent is2-methylpiperidine. a I

6;- Themethod of-claim- 1 wherein saidfuel component comprises2,3-dimethylpiperidine.,

7. The method of claim 1 .wherein'said fuel. componentcomprises,2,4-dirnethylpipcridine.

8. The method of claimr l wherein said. fuel; component comprises,2,2-dimethylpiperidine.

9. A method for producingimmediate. ,thrustcomptfiing simultaneouslyintroducing separate streams 10f an oxidantcomponent and a fuelcomponent of a bipropel; lantinto contact with. each other inracombustiomghamber of a reaction motor intsuchi proportions as toproducespontaneousignition, said ,fuel :compouentv comprising a 2-alkylsubstituted piperidineiwherein thezalkylrgroup con tains notmore than 12carbon.atomssandwhfireinithelotal number of carbon atomsiinthepiperidine moleeule isinot greater. than :17...

10. VA- .methoddor producing; immedia e 1 t o-18 n G9 3-prisingsimultaneonsly introducing separate rstrearns ,2 pi @i] oxidantcomponentand a fuel ,component ofqa bipropel; lant into contact.withcachother in; a comhustion --;cham; ber-loft atreactionimotorvin;suchqproportionsras tQrPI 1199 spontaneous r ignition, said. fuel .;comp0n nt c mprisi ssa 2,4;alky1l substituted. piperidine wherein AlSlllJ- itl ll alkyl group contains gnotsmore than. 121carbon atomswhereinnthestotal numberoi carbon atoms: a dine molecule shoot-greater:than 17 4am weet- Fara-F 225 2,512,227 Biswel l e 5 2, 2 ,471] a a

1. A METOD FOR PRODUCING IMMEDIATE THRUST COMPRISING SIMULTANEOUSLYINTRODUCING SEPARATE STREAMS OF AN OXIDANT COMPONENT AND A FUELCOMPONENT OF A BIPROPELLANT INTO CONTACT WITH EACH OTHER IN A COMBUSTIONCHAMBER OF A REACTION MOTOR IN SUCH PROPORTIONS AS TO PRODUCESPONTANEOUS IGNITION, SAID FUEL COMPONENT COMPRISING A PIPERIDINECHARACTERIZED BY THE STRUCTURAL FORMULA